Seat reclining mechanism

ABSTRACT

A seat reclining mechanism including a cushion arm pivotally connected to a squab arm by a planetary gear arrangement, the planetary gear arrangement including a pair of side by side ring gears, one of the ring gears being secured to the squab arm and the other of the ring gears being secured to the cushion arm, a sun and planetary gear arrangement common to both ring gears, the sun and planetary gear arrangement including a plurality of radially movable planetary gears surrounding a sun gear assembly, the sun gear assembly including at least one axially movable frusto-conical sun gear in engagement with said planetary gears, the at least one frusto-conical sun gear being axially biased so as to bias sun gear member into full meshing contact with the planetary gears and thereby bias the planetary gears in a radially outwards direction to a radially outermost position whereat the planetary gears are in full meshing contact with said ring gears, the sun gear assembly including a stop sun gear axially juxtaposed to said frusto-conical sun gear, said stop sun gear being in partial meshing contact with said planetary gears when at their radially outermost position such that the planetary gears are able to move radially inwards against said bias to a radially innermost position defined by the stop sun gear whereat the planetary gears are in full meshing contact with said stop sun gear.

The present invention relates to a seat reclining mechanism. In our UKpatents 1528357 and 1586869 we disclose a seat reclining mechanism whichincludes a cushion arm pivotally connected to a squab arm by a planetarygear arrangement. The planetary gear arrangement includes a pair of sideby side ring gears, one being secured to the squab arm and the otherbeing secured to the cushion arm. A sun gear is provided which is indriving connection with both ring gears via a plurality of planetarygears. The pitch of teeth in each of the ring gears is different so thatrotation of the planetary gears causes relative rotation between thering gears.

The planetary gears float and it is necessary for there to be anacceptable amount of tolerance between the gears in order to enablesmooth operation. Unfortunately such tolerance also results in pivotalplay between the squab and cushion arms.

According to the present invention there is provided a seat recliningmechanism including a cushion arm pivotally connected to a squab arm bya planetary gear arrangement, the planetary gear arrangement including apair of side by side ring gears, one of the ring gears being secured tothe squab arm and the other of the ring gears being secured to thecushion arm, a sun and planetary gear arrangement common to both ringgears, the sun and planetary gear arrangement including a plurality ofradially movable planetary gears surrounding a sun gear assembly, thesun gear assembly including at least one axially movable frusto-conicalsun gear in engagement with said planetary gears, the at least onefrusto-conical sun gear being axially biased so as to bias sun gearmember into full meshing contact with the planetary gears and therebybias the planetary gears in a radially outwards direction to a radiallyoutermost position whereat the planetary gears are in full meshingcontact with said ring gears, the sun gear assembly including a stop sungear axially juxtaposed to said frusto-conical sun gear, said stop sungear being in partial meshing contact with said planetary gears when attheir radially outermost position such that the planetary gears are ableto move radially inwards against said bias to a radially innermostposition defined by the stop sun gear whereat the planetary gears are infull meshing contact with said stop sun gear.

Accordingly when the sun gear assembly is static pivotal play betweenthe squab arm and cushion arm is substantially reduced or eliminated byvirtue of the planetary gears being radially biased outwardly intocontact with the ring gears by the frusto-conical sun gear. In addition,when under radial loading, as for example when the sun gear assembly isdriven, the planetary gears are able to move radially inwardly into fullmesh with the stop sun gear. This provides a positive smooth drive fromthe sun gear assembly to the planetary gears.

Preferably a pair of frusto-conical sun gears are provided arranged withtheir smaller diameter axial ends facing one another and such that theyare located on opposite axial sides of the planetary gears. The biasingmeans are arranged such as to urge the two frusto-conical sun gearsaxially toward one another. This may be achieved by having onefrusto-conical sun gear axially fixed and the other axially movable orboth frusto-conical sun gears may be axially movable.

Preferably three planetary gears are provided which are equally spacedabout the internal circumference of the ring gears. Three planetarygears are preferred since such an arrangement ensures that each sun gearwill apply an equal radial loading on each planetary gear. However it isto be appreciated that more than three planetary gears may be providedif necessary.

The mechanism may also include at least one support member for theplanetary gears of the type disclosed in our UK patent 1586869. Thus thesupport member would include for each planetary gear a concave surface.

In the present invention, the support member serves primarily tomaintain the circumferential spacing of the planetary gears whilst theplanetary gears are located between their radially inner and outermostpositions. Preferably the support member is arranged to supplementaccommodation of radially inwardly directed loadings when the planetarygears are located at their radially innermost positions. Such anarrangement enables the mechanism to withstand excessive radiallyinwardly directed loadings as may for example arise during a vehiclecrash.

Preferably the included angle between the inclined peripheral face ofeach frusto-conical sun gear and its axis is small, for example in therange 2° to 15°.

Preferably the frusto-conical sun gear, stop sun gear and planetarygears have involute teeth. This facilitates smooth operation of themechanism.

The frusto-conical sun gear and stop sun gear may be separate componentslocated axially side by side, or alternatively the frusto-conical sungear and stop sun gear may be integrally formed.

Various aspects of the present invention are hereinafter described withreference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a vehicle seat including aseat reclining mechanism according to the present invention;

FIG. 2 is a schematic side view of a seat reclining mechanism accordingto the present invention;

FIG. 3 is a more detailed part sectional view taken along line III—IIIin FIG. 2; and

FIG. 4 is a part sectional view taken along line IV—IV in FIG. 3;

FIG. 5 is a side view of a sun gear according to one embodiment of theinvention;

FIG. 6 is a section along line VI—VI in FIG. 5;

FIG. 7 is a section along line VII—VII in FIG. 5;

FIGS. 8a, 8 b schematically illustrate location of a planetary gear at aradially outermost position and radially innermost positionrespectively;

FIG. 9 is an axial sectional view similar to FIG. 3 showing a furtherembodiment according to the present invention; and

FIG. 10 is an axial sectional view similar to FIG. 3 showing a furtherembodiment according to the present invention.

The seat reclining mechanism 10 of the present invention is used topivotally connect a seat back or squab 8 to a seat cushion 7. Althoughone mechanism 10 can be used per seat, preferably two mechanisms 10 areused, one being located on either side of the seat(only one of which isvisible in FIG. 1) and each mechanism 10 includes a squab arm 13 securedto the frame (not shown) of the squab and a cushion arm 15 secured tothe frame (not shown) of the cushion. The mechanisms are both driven bya handle 9.

In the embodiment illustrated, the mechanism includes a first ring gear12 which forms part of the squab arm 13 (only part of which is visiblein FIG. 2) and a second ring gear 14 which forms part of a cushion arm15 (only part of which is visible in FIG. 2). The squab and cushion armsare more fully illustrated in our UK patents 1528357 and 1586869.

The squab and cushion arms are preferably formed from metal plate andthe ring gears 12, 14 are preferably formed by a pressing operation. Thepressing operation provides offset wall portions 13 a, 15 a whichtogether with the internal walls of the ring gears define a housing forthe sun and planetary gears 16 and 18 respectively.

As seen in FIG. 4, three planetary gears 18 are provided which areequi-spaced about the internal circumference of the ring gears 12, 14.

As seen in FIG. 3 the mechanism preferably includes a pair of identicalsun gears 16′, 16″. A single sun gear 16 is shown in greater detail inFIGS. 5 to 7 from which it will be seen that each gear 16 includes afrusto-conical gear portion 16 a and an axially juxtaposed cylindricalgear portion 16 b.

Each gear 16′, 16″ is axially slidably received on a drive shaft 20 soas to be rotatable in unison therewith. Each gear 16′, 16″ is urgedaxially toward one another by associated springs 110.

As seen in FIG. 3 the drive shaft 20 includes a main portion 20 a whichextends through the hinge assembly. The main portion 20 a is preferablyfluted to define in cross-section a star shape (see FIG. 4). At one sideof the hinge assembly the main portion 20 a is provided with a shoulder121 which is preferably formed integrally with the main portion 20 a. Acoil spring 110 is compressed between the shoulder 121 and sun gear 16′.This has the effect of biasing sun gear, 16′ in an axial directiontoward sun gear 16″.

At the opposite side of the hinge assembly the main portion 20 a isprovided with a cap 125. The cap 125 includes an internal bore 126 whichhas a portion having a cross-sectional shape complementary with the mainportion 20 a and so is rotatable in unison therewith. The cap 125 isheld axially captive on the shaft by a nut 128. The cap 125 comprises adog of conventional brake unit 130 which in use acts to resistregression of the hinge assembly.

A coiled spring 110 is compressed between cap 125 and sun gear 16″. Thishas the effect of biasing the sun gear 16″ in an axial direction towardsun gear 16′.

As seen in FIG. 5 each sun gear 16′, 16″ has a central bore 16 d havinga cross-sectional shape complementary with the cross-sectional shape ofthe shaft portion 20 a which enables each sun gear to slide axiallyalong the main shaft portion 20 a and yet be rotationally fixed relativethereto. Preferably the star shape of the main shaft portion 20 a andsun gear bore is chosen to have the same number of star arms as thenumber of teeth on the sun gear, the star arms being radially alignedwith the teeth. This facilitates ensuring that both sun gears 16′, 16″are correctly aligned during assembly of the mechanism.

However, it will be appreciated that other cross-sectional shapes of themain shaft 20 a may be adopted if desired, such as for example apolygonal shape.

Accordingly, as more clearly shown in FIG. 8a, the frusto-conical gearportion 16 a of each gear 16′, 16″ is urged into contact with theplanetary gears 18 and this has the effect of urging the planetary gears18 in a radially outwards direction to engage the ring gears 12, 14. Thesprings 110 therefore serve to remove play between the gears 12, 14, 16and 18.

Under certain circumstances, radially inwardly directed loadings areapplied onto the planetary gears 18. This, for example, can arise duringdriving of the sun gears 16′, 16″ when adjusting the pivotal anglebetween arms 13, 15 whilst a load is applied onto one of the arms 13,15.

Under such circumstances, the planetary gears 18 are permitted to moveradially inwardly to displace the sun gears 16′, 16″ axially against thebias of springs 110 and thereby enable the planetary gears to mesh infull contact with the cylindrical gear portions 16 b. This isillustrated in FIG. 8b. In this condition, drive is smoothly transmittedfrom the sun gears 16′, 16″ to the ring gears 12, 14 via the planetarygears 18. In addition, once the planetary gears 18 are fully seated onthe cylindrical gear portions 16 b further radially directed loadingsare transmitted to the drive shaft without causing additional axialdisplacement of the sun gears 16′, 16″.

Accordingly, under static conditions the influence of the bias of spring110 causes each frusto-conical gear portion 16 a to move the planetarygears 18 radially outwardly and maintain the planetary gears 18 at aradially outermost position ( FIG. 8a) whereat the planetary gears arein full mesh contact with the ring gears 12, 14 and gear portion 16 awhereas under dynamic conditions, such as during adjustment of themechanism under applied loadings, the bias of springs 110 is preferablychosen to be insufficient to overcome radially inwardly directedloadings on the planetary gears such that the planetary gears 18 areable to move radially inwardly to a radial innermost position (FIG. 8b)whereat the planetary gears 18 are in full mesh contact with thecylindrical gear portions 16 b.

The planetary gears 18 are each of cylindrical form and the angle ofinclination for the frustoconical gear portion 16 a is chosen bearing inmind the functional requirement for the sun gears 16′, 16″ to be capableof being moved axially outward by the planetary gears and being movedaxially inward by the bias of springs 110.

Accordingly, the angle of inclination adopted is preferably greater than0° and less than about 45°. The greater the angle of inclination, thestronger the biasing force required to be generated by springs 110.

It is generally desirable for springs 110 to generate a low biasingforce in order to reduce operating torques and so it is preferable forthe angle to range between about 1° to about 15°. In a typicalarrangement, the angle of inclination adopted is about 10° and thebiasing force applied by the springs 110 is about 40 Newtons.

Preferably each gear 16′, 16″ is provided with a boss portion 16 clocated on its outer side so as to provide an axial extension to itsaxial. bore 16 d and thereby provide greater resistance to twisting ofeach gear 16′, 16″ when under load.

It is envisaged that the edges of the planetary gears 18 may bechamfered slightly to assist axial entry of each sun gear 16 withoutinterfering with the rolling action of the gears.

It will be seen in FIG. 4 that the gear profiles are involute. Thisprovides for smooth operation of the mechanisms since the planetarygears and ring gears are maintained in rolling contact. If desiredhowever the gear profiles adopted in our UK patents 1528357 and 1586869may be used.

It is envisaged that only one of the sun gears 16′ or 16″ includes acylindrical portion 16 b. It is also envisaged that the sun gears 16′and 16″ comprise frusto-conical portions 16 a only and that a separatecylindrical sun gear portion 16 b be located inbetween the sun gears16′, 16″.

It is also envisaged that only one sun gear 16 be provided. Such anembodiment 100 is illustrated in FIG. 9 wherein parts similar to thosedescribed in connection with FIGS. 1 to 8 have been designated by thesame reference numerals.

A further embodiment 300 is illustrated in FIG. 10 which illustrates amechanism in which a single sun gear 16 is provided having afrusto-conical portion 16 a only and in which a separate cylindricalgear 16 b is provided. Again parts similar to those described inconnection with FIGS. 1 to 8 have been designated by the same referencenumerals.

If desired a support member 200 (FIGS. 3 and 4) may be included. Thesupport member has concave depressions 201 in each of which a planetarygear 18 is seated. The depressions 201 in the support member 200 serveto guide rotary movement of the planetary gears and maintain theircircumferential spacing.

The shape and dimensions of the depressions 201 are chosen such that thesupport member 200 does not interfere with the planetary gears 18 movingradially inwardly to their radial innermost position (FIG. 8b) but doprovide additional support to prevent radial inward movement beyond saidinnermost position in the event of excessive loadings.

As illustrated in the drawings, three planetary gears 18 are preferred.This is because three is the minimum number of gears which can be actedupon by the sun gear(s) to ensure that the sun gear(s) apply an equalload to all planetary gears irrespective of the concentricity of thering gears 12, 14 and/or the circularity of each ring gear 12, 14.

If a larger number of equally spaced planetary gears 18 are to be used,preferably the number is chosen such that no two gears are diametricallyopposed ie an odd number of gears is chosen.

In the embodiments described above and illustrated in the drawings, thepivotal movement between the squab and cushion arms is defined andsupport by the gear system, ie by the intermeshing of the sun, planetaryand ring gears and there is no separate journal for supporting thepivotal movement. It will be appreciated however that the squab andcushion arms could be pivotally connected by journal formations and thatthe sun, planetary and ring gears be utilised to cause relative rotationabout the pivot only.

What is claimed is:
 1. A seat reclining mechanism including a cushionarm pivotally connected to a squab arm by a planetary gear arrangement,the planetary gear arrangement including a pair of side by side ringgears, one of the ring gears being secured to the squab arm and theother of the ring gears being secured to the cushion arm, a sun andplanetary gear arrangement common to both ring gears, the sun andplanetary gear arrangement including a plurality of radially movableplanetary gears surrounding a sun gear assembly, the sun gear assemblyincluding at least one axially movable frusto-conical sun gear inengagement with said planetary gears, biasing means for biasing the atleast one frusto-conical sun gear axially so as to bias said sun gearinto full meshing contact with the planetary gears and thereby bias theplanetary gears in a radially outward direction to a radially outermostposition whereat the planetary gears are in full meshing contact withsaid ring gears, the sun gear assembly including a generally cylindricalstop sun gear axially juxtaposed to said frusto-conical sun gear, saidstop sun gear being in partial meshing contact with said planetary gearswhen at their radially outermost position the biasing means beingarranged such that during operation of the seat reclining mechanism theplanetary gears are able to move radially inwards against said bias to aradially innermost position defined by the stop sun gear whereat theplanetary gears are in full meshing contact with said stop sun gear. 2.A mechanism according to claim 1 wherein a pair of frusto-conical sungears are provided arranged with their smaller axial ends facing oneanother and such that they are located on opposite axial sides of theplanetary gears.
 3. A mechanism according to claim 2 wherein the biasingmeans are arranged such as to urge the two frusto-conical sun gearsaxially toward one another.
 4. A mechanism according to claim 3 whereinone frusto-conical gear is axially fixed and the other is axiallymovable by said biasing means.
 5. A mechanism according to claim 3wherein both frusto-conical gears are axially movable by said biasingmeans.
 6. A mechanism according to claim 1 further including threeplanetary gears equally spaced about the internal circumference of thering gears.
 7. A mechanism according to claim 1 further including atleast one support member for the planetary gears, the support memberhaving a recess defined by a concave surface for each planetary gear,the support member serving to maintain the circumferential spacingbetween the planetary gears whilst the planetary gears are locatedbetween their radially inner and outermost positions.
 8. A mechanismaccording to claim 1 wherein the support member is arranged tosupplement accommodation of radially inwardly directed loadings when theplanetary gears are located at their radially innermost positions.
 9. Amechanism according to claim 1 wherein an included angle between aninclined peripheral face of east frusto-conical sun gear and its axis isin the range of 2° to 15°.
 10. A mechanism according to claim 1 whereinthe stop gear is integrally formed with the at least one sun gear.
 11. Amechanism according to claim 1 wherein the stop sun gear is a separatecomponent located axially side by side with the at least one sun gear.